1. Field Of The Invention
This invention relates to a polyurethane film-forming composition of a polyisocyanate, a polymer having pendent hydroxyl-containing groups, and a reactive plasticizer.
2. Description Of The Prior Art
Polyurethane compositions are conventionally used as coatings, adhesives and molding materials. The inclusion in these compositions of a hydroxyl-containing polymer and a polyisocyanate is shown, for example, by U.S. Pat. No. 3,245,941 issued Apr. 12, 1966 to Mayer, et al. Such compositions are useful as coatings and the like but do not provide the durability and flexibility required for industrial finishes.
U.S. Pat. No. 3,558,564 issued Jan. 26, 1971 to Vasta shows a polyurethane coating of a polyisocyanate and a hydroxyl-containing polymer which satisfies these requirements. The hydroxyl groups shown in this patent are contained in ester groups attached directly to the polymer backbone, the ester groups being formed by reacting a hydroxyalkyl monomer, an anhydride of a dicarboxylic acid, and a glycidyl ester. These ester groups give the coating excellent flexibility but add to the molecular weight of the polymer, making it difficult to apply by spraying at high volume-solids, above 50%.
With the current emphasis on reduced solvent emissions and lower energy consumption, there remains a need for a polyurethane coating which not only can be spray-applied at high volume-solids but also can be cured at ambient temperatures to form a durable, flexible finish.